There is known a sample analysis element using localized surface plasmon resonance (LSPR). Such a sample analysis element is provided with, for example, metal nanobodies distributed on a dielectric surface, namely a metal nanostructure. The metal nanostructure is formed to be sufficiently smaller than the wavelength of excitation light, for example. When the metal nanoparticles are irradiated with the excitation light, all electrical dipoles are aligned, and thus an enhanced electrical field is induced. As a result, near-field light is generated on the surface of the metal nanostructure. So-called hot spots are formed.
In Yizhuo Chu et al., “Experimental study of the interaction between localized and propagating surface plasmons,” OPTICS LETTERS, U.S., Feb. 1, 2009, Vol. 34, No. 3, pp. 244-246, the metal nanostructure is arranged at a predetermined pitch forming a grid pattern. If the dimension of the pitch is set to a specific numerical value, a propagating surface plasmon resonance (PSPR) is caused based on an evanescent wave. The propagating surface plasmon resonance unites with the localized surface plasmon resonance. A so-called hybrid mode is established. In such a manner as described above, the localized surface plasmon resonance is enhanced by the propagating surface plasmon resonance, and thus, the near-field light is enhanced on the surface of the metal nanostructure.